Internal combustion engine fuel supply system

ABSTRACT

A system to supply hydrogen-rich fuel to an internal combustion engine, whereby a hydrogen-rich gas is produced from a liquid raw fuel by a hydrogen generator. The exhaust line of the internal combustion engine contains an exhaust purification system, such as a DeNOx catalytic converter, which is at least temporarily supplied with hydrogen-rich gas through a bypass line. In addition, the exhaust line is in thermal contact with the hydrogen generator in order to recover thermal energy.

FIELD OF THE INVENTION

The invention concerns a system for supplying fuel to an internalcombustion engine.

DESCRIPTION OF THE RELATED ART

A goal in the development of motor vehicles with internal combustionengines today is the reduction of fuel consumption and carbon dioxideemissions. It is also desired to reduce other pollutants in the exhaust,in particular nitrogen oxides (NOx).

Motor vehicles with cracking carburetors, in which hydrocarbon fuels areconverted by a partial oxidation device prior to entering the internalcombustion engine, are well known. However, this conversion processtypically requires temperatures over 800° C., resulting in the formationof soot particulates. In addition, the exothermic nature of the reactionleads to an energy loss during the chemical conversion.

DeNOx (nitrogen oxide removal) catalytic converters, which reducenitrogen oxides in the exhaust by converting the nitrogen oxides tonitrogen with a suitable catalyst and reducing agents, are known. Inthis regard, it is well known to produce hydrogen and carbon monoxideon-board the vehicle from hydrocarbons or urea. The use of urea requiresa separate urea tank.

There remains a need to reduce the fuel consumption and emissions ofinternal combustion engines.

BRIEF SUMMARY OF THE INVENTION

The present system includes a hydrogen generator to produce ahydrogen-rich fuel for combustion in an internal combustion engine. Thehydrogen-rich fuel may also be used in a downstream DeNOx catalyticconverter to reduce the NOx content of the engine exhaust. Heat isrecovered from the exhaust stream and supplied to the hydrogen generatorto support the endothermic conversion of raw fuel to the hydrogen-richfuel.

Using endothermic reactions during the production of hydrogen-rich fuelincreases the calorific value of the reactants by the amount of energyrecovered from the engine exhaust. This leads to a correspondinglyhigher overall efficiency of the whole system, which goes hand in handwith a reduction in carbon monoxide emissions.

Hydrogen-rich fuel produced by endothermic steam reforming in additionto being suitable for combustion in the internal combustion engine, isparticularly useful as a reducing agent in a DeNOx catalytic converter.The increased nitrogen output, which in the case of methanol—due to thehigh purity of the fuel—predominantly consists of thermal nitrogenoxides, can be reduced by a DeNOx catalytic converter in combinationwith the use of the produced hydrogen-rich fuel as a reducing agent.This makes it possible to increase the combustion temperature, and thusthe efficiency, of the internal combustion engine.

In addition to conventional fuels, such as gasoline and diesel,alternative fuels, such as methanol, dimethyl ether (“DME”), or ethanol,are suitable for use. Methanol in particular, but also DME, can beconverted to a hydrogen-rich fuel at low temperatures. The hydrogen-richfuel is predominantly composed of hydrogen, carbon monoxide, andpossibly some unconverted fuel. The low temperatures simplify theselection of the raw fuel and promote the recovery of thermal energyfrom the engine exhaust. When using methanol, for example, an energyrecovery rate of approximately 20% can be achieved using the engineexhaust alone. For conversion of hydrocarbon fuels, similar amounts ofenergy have to be transferred at significantly higher temperatures, sothat the energy content and the temperature level are potentially onlysufficient to partially convert the fuel.

Particularly in the case of methanol, but also for DME, no sootparticulates, or only very small quantities, are produced during theconversion. Similarly, the combustion of the resultant mixtures ofhydrogen and carbon monoxide, and possibly unconverted fuelconstituents, in the internal combustion engine does not create anyproblems with respect to the formation of pollutants, including sootparticulates. This system is a gas engine, with all the well-knownadvantages related to mixture formation and combustion. Furthermore,methanol and DME are very pure substances, so that the combustion andthe exhaust purification are not contaminated by other unwantedsubstances, such as sulphur.

All of the listed fuels can be generated from natural gas, or as arenewable resource, from biomass. This contributes to the long-termreduction of global carbon dioxide levels. In particular alcohols andDME produce less carbon dioxide, simply due to their lower carboncontent per unit of energy released.

The corrosive properties of the raw fuels are not a problem in theinternal combustion engine since the conversion into hydrogen and carbonmonoxide takes place under conditions that are entirely different fromthose of combustion in an internal combustion engine. Moreover, hydrogenand carbon dioxide are not corrosive.

Possible disadvantages of the hydrogen generator during a cold-start orload changes can be avoided by directly combusting the raw fuels in theinternal combustion engine when these conditions arise.

These and other aspects will be evident upon reference to the attachedFigure and following detailed description.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a schematic diagram of an embodiment of the present system forsupplying fuel to an internal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

Raw fuel, preferably in liquid form, is carried in a vehicle in a tank1, and is fed to a hydrogen generator 3 (e.g. a reformer) by a raw fuelfeed line 2. Raw fuel feed line 2 contains a pump 4, which pumps andpossibly meters the raw fuel. In hydrogen generator 3, an endothermicreaction converts the raw fuel into a gaseous hydrogen-rich fuel, whichis then supplied to an internal combustion engine 5 through ahydrogen-rich fuel feed line 6. To regulate the amount of hydrogen-richfuel supplied, the hydrogen-rich fuel feed line is equipped with a firstvalve 11. Air required for combustion is supplied to internal combustionengine 5 through an-intake line 7. After combustion, the exhaust isdischarged through an exhaust line 8.

Exhaust line 8 contains an exhaust purification system 9, preferably aDeNOx catalytic converter, in which nitrogen oxides contained in theexhaust are reduced to nitrogen using reducing agents present in theexhaust.

To supply or to increase the amount of the reducing agents in theexhaust, a hydrogen-rich fuel bypass line 10 is disposed to connecthydrogen-rich fuel feed line 6 to exhaust line 8, upstream of exhaustpurification system 9. The hydrogen-rich fuel from fuel feed line 6 isallowed to mix with the exhaust in line 8 upstream of exhaustpurification system 9. Alternatively, hydrogen-rich fuel bypass line 10may directly lead into exhaust purification system 9. In addition,hydrogen-rich fuel bypass line 10 contains a second valve 16, to adjustthe quantity of hydrogen-rich fuel to be supplied to exhaustpurification system 9.

Since the reaction that takes place in the hydrogen generator is anendothermic reaction, it is necessary to heat hydrogen generator 3, andaccordingly, hydrogen generator 3 in the representative embodimentillustrated in FIG. 1 is integrated into a heat exchanger 12. Heatexchanger 12 includes a heating chamber 13, which is in thermal contactwith hydrogen generator 3 through a separating wall 14. Heating chamber13 is integrated into exhaust line 8 downstream of exhaust purificationsystem 9, so that exhaust passes through heating chamber 13,transferring thermal energy from the exhaust to the reaction zone ofhydrogen generator 3. After passing through heating chamber 13, theexhaust may be discharged to the surroundings.

In addition to the embodiment illustrated in FIG. 1, otherconfigurations are possible to transfer thermal energy from the exhaustto hydrogen generator 3. For example, a heat exchanger may be includedin raw fuel feed line 2, upstream of hydrogen generator 3, so that thetransferred thermal energy is introduced into hydrogen generator 3 bythe reactants. It is also possible to interpose an additionalheat-exchanging medium so heat is transferred indirectly to the rawfuel.

Typically, the liquid raw fuel is evaporated and possibly superheated inan evaporator 15 before entering hydrogen generator 3. For this purpose,evaporator 15 may be configured analogously to heat exchanger 12,whereby an evaporation chamber 17 is in thermal contact with a heatingchamber 19 through a separating wall 18. Exhaust flows through heatingchamber 19, which is integrated in exhaust line 8. The exhaust may passthrough heating chambers 13 and 19 of heat exchangers 12 and 15 inseries. Alternatively, a bypass line 20 may branch off exhaust line 8upstream of heat exchanger 12, and may rejoin exhaust line 8 between theheat exchangers 12 and 15. In this case, the flow passes through heatexchangers 12 and 15 at least partially in parallel. Alternatively, theflow may be directed through heat exchangers 12 and 15 entirely inparallel. In this case, the heating chamber associated with hydrogengenerator 3 is integrated in exhaust line 8, while heating chamber 19associated with evaporation chamber 17 is arranged in bypass line 20,and bypass line 20 joins exhaust line 8 downstream of evaporator 15.

Alternatively, part of the thermal energy required for evaporating theraw fuel and/or the water may be obtained from the cooling system ofinternal combustion engine 5.

In an alternative embodiment (not shown), depending on the desiredtemperature level, exhaust purification system 9 can also be located inexhaust line 8 downstream of heat exchanger 12 and/or heat exchanger 15.

In still another embodiment, a sound absorber 21 may be disposed inexhaust line 8. Furthermore, hydrogen-rich fuel feed line 6 may containa further heat exchanger 22, which is charged with a cooling medium tocool the hydrogen-rich fuel issuing from hydrogen generator 3. Finally,a storage container 23 for hydrogen-rich fuel may be provided, which isconnected to hydrogen-rich fuel feed line 6. Preferably, storagecontainer 23 is connected to hydrogen-rich fuel feed line 6 downstreamof heat exchanger 22, so that only cooled hydrogen-rich fuel is suppliedinto the storage container 23, thereby increasing the storage capacityof storage container 23.

The pressure in hydrogen-rich fuel feed line 6 usually is only slightlyhigher than ambient pressure. To improve the dynamic behaviour and toimprove the dosing, the pressure may be at a slightly higher level,preferably at an excess pressure of between 1 to 10 bar.

In a further embodiment, internal combustion engine 5 may be connectedwith tank 1 by an additional raw fuel feed line 2 a, so that liquid rawfuel can be directly supplied to internal combustion engine 5. In thiscase, in the event of rapid load changes and/or during a cold start,part or all of the fuel provided directly to internal combustion engine5 can be liquid raw fuel. For this purpose, a third valve 24 is arrangedin raw fuel feed line 2 a.

Typical fuels include alcohols or other fuels that can be crackedcatalytically or thermally, such as methanol, dimethyl ether, ethanol,gasoline, and diesel.

Depending on the fuel employed, various material conversion processescan take place in hydrogen generator 3. In the case of methanol, theseare:

Pyrolysis:CH₃OH→CO+2H₂

Steam reforming:CH₃OH+H₂O→CO₂+3H₂

Both reactions preferably take place on conventional copper catalysts attemperatures above 200° C. and with a heat input of approximately 4000kJ/kg. Steam reforming has the advantage that the formation of sootparticulates is suppressed. Further, hydrogen and carbon dioxide areproduced as hydrogen-rich fuel, but only small amounts of toxic carbonmonoxide are formed. The methanol can be evaporated together with thewater in evaporator 15, which suppresses coking of evaporator 15. Onedisadvantage of steam reforming is the higher evaporation energyrequirement, which is due to the fact that a larger, more expensive,device is needed. Moreover, if the water is to be carried along in thetank, the dimensions of the tank need to be larger. As an alternative,the water can be reclaimed from the exhaust. However, this technology istechnically complicated and thus expensive. If a combination ofpyrolysis and steam reforming is used, the overall process can beoptimized with respect to tank size, evaporation energy requirements andthe endothermic conversion, size of the required equipment, and therequired energy content and temperature of the exhaust.

If ethanol is used, which has a higher calorific value than methanol,the reactions are:

Pyrolysis:C₂H₅OH→CO+3H₂+C

Steam reforming:C₂H₅OH+H₂O→2CO+4H₂

Both reactions take place at temperatures above 500° C. Again, anadvantage of steam reforming is the lower risk of forming sootparticulates. Evaporating ethanol and water together can reduce cokingof the evaporator. An increased supply of water can further reduceparticulate formation and at the same time helps to convert part of thecarbon monoxide into carbon dioxide and hydrogen in a shift reaction.The disadvantages of steam reforming are the same for methanol andethanol, and are discussed above.

If a fuel such as dimethyl ether (DME) is used, the fact that it isgaseous under normal ambient conditions must be taken into account.However, DME liquefies at low pressure and accordingly may be carried asa liquid in a pressure tank at comparatively low pressure.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A system for supplying fuel to an internal combustion engine havingan exhaust line, the system comprising: a tank to store raw fuel, ahydrogen generator to convert the raw fuel to a gaseous hydrogen-richfuel, a raw fuel feed line between the tank and the hydrogen generator,a pump disposed in the raw fuel feed line, a hydrogen-rich fuel feedline between the hydrogen generator and the internal combustion engine,an exhaust purification system disposed in the exhaust line, ahydrogen-rich fuel bypass line configured to connect the hydrogen-richfuel feed line to one of the exhaust purification system or the exhaustline upstream of the exhaust purification system, and a valve disposedwithin the hydrogen-rich fuel bypass line, wherein the hydrogengenerator is in thermal contact with the exhaust line.
 2. The system ofclaim 1, further comprising an evaporator disposed in the raw fuel feedline between the pump and the hydrogen generator.
 3. The system of claim2, wherein the evaporator is in thermal contact with the exhaust line.4. The system of claim 3, wherein the evaporator is in thermal contactwith the exhaust line downstream of the hydrogen generator, with respectto the flow direction of the exhaust.
 5. The system of claim 3, whereinthe exhaust line comprises a main exhaust line comprising the exhaustpurification system and an exhaust bypass line, wherein both thehydrogen generator and the evaporator are in thermal contact with theexhaust bypass line.
 6. The system of claim 2, wherein the internalcombustion engine has a cooling system and wherein the evaporator is inthermal contact with the cooling system.
 7. The system of claim 1,further comprising a heat exchanger disposed in the hydrogen-rich fuelfeed line.
 8. The system of claim 1, further comprising a storagecontainer connected to the hydrogen-rich fuel feed line.
 9. The systemof claim 1, further comprising a raw fuel feed line between the tank andthe internal combustion engine.
 10. The system of claim 1, wherein theexhaust purification system comprises a DeNOx catalytic converter.